Identifying diatom indicator species of nutrient enrichment: An in situ nutrient enrichment experiment in subtropical upland streams

Nutrients are a fundamental determinant of broad scale patterns in the benthic algal community of stream ecosystems. Excessive inputs of nutrients such as nitrogen and phosphorus into upland streams may result in significant impacts on benthic algal communities. In upland streams, diatoms are the most abundant and diverse taxonomic group in benthic algal communities. In this study, benthic algal biomass and diatom community responses to in situ nitrogen and phosphorus enrichment were investigated by conducting an in-stream nutrient diffusing substrate experiment at high and low ambient nutrient concentration sites. Nitrogen was found to be the primary limiting nutrient across all sites, regardless of the ambient nutrient concentrations. In general, enrichment relieved nutrient limitation, promoting the dominance of a smaller suite of eutrophic species in the community. This was particularly evident in the low ambient nutrient sites where oligotrophic species initially dominated the community. This study identified diatom species with competitive advantage under nutrient enriched conditions and further the understanding of diatom species competition for multiple nutrients. Five diatom nutrient trait groups differentiate nutrient generalists and specialists and identifies potential indicator species based on their responses to specific enrichment treatments.